Abstract

Characteristics of plasma nitriding and nitrocarburizing for steam treated sintered steels were studied. Fe-0.8%C powder containing Ni, Cu were sintered at 1120°C and steamed at 520°C. Temperature of plasma nitriding and nitrocarburizing was varied from 500°C to 600°C. Gas mixture of nitriding was set at N_2 : H_2 =80:20 (vol.%), but CH_4gas was added 1~2 vol.% for nitrocarburizing. Steam treatment for sintered steels brought not only the formation of oxide layer but also decarburizing near the surface. Decrease in hardness near the surface resulted from the formation of ferrite due to decarburizing. Thus, the low hardness was recovered not with plasma nitriding but with plasma nitrocarburixing. Wear resistance properties of steamed specimens and ni-trocarburized specimens were better than those of nitrided specimens according to the pin-on-disk wear test. On the other hand, the fatigue life of steamed specimen was shorter than that of nitrocaiburized specimen.